This invention relates to an optical recording member for storing data by the selective ablation of a layer of energy absorbing material by laser address and more particularly, to a recording member having a layer of energy absorbing material and layer of a polymeric material contiguous recording layer.
Digital storage systems are known which utilize optical methods including a recording member wherein digital information is written by the selective ablation of an energy absorbing material which forms a part of the recording member. The ablation of the energy absorbing material is achieved by the relative motion between the recording member and a laser beam which is modulated by a signal representative of the information to be stored.
Recording members including a substrate, an energy absorbing layer, and a coating over the energy absorbing layer are known in the art. Such optical storage devices are extremely advantageous because of the large amount of information that can be stored in a relatively small physical area when compared with known storage methods such as, for example, magnetic tape.
A disadvantage of optical recording members such as the above is that uncoated energy absorbing layers are subject to physical damage because of handling under the conditions of use including wear, abrasion and the presence of unwanted dust and dirt particles. Because of the high density of the information being stored on the optical recording member, any foreign particle of dust or dirt can create a false signal which would be read as a bit of information stored in the device. For this reason, it is desirable to overcoat the recording layer prior to the storing of the digital data in the recording member. In one embodiment, polymeric overcoatings have been employed as protective layers over the recording member.
A disadvantage in the use of overcoatings in contact with the recording layer is that the energy requirements for marking the recording layer in accordance with the modulated signal imparted to the laser are greatly increased when the polymer coating is in place. Thus, in order to create an ablated portion of the recording member in accordance with a signal representing a bit of digital information, more energy must be imparted to the recording member than when no overcoat is employed. In general, an increase on the order of three or four times or higher is required in order to write the information into the recording member. The minimum amount of energy required to create the ablated pit in the recording member is termed the threshold energy. It is desirable to maintain this threshold as close to that required to ablate the recording layer disposed on a substrate without an overcoat being present.
Accordingly, it is a primary object of the present invention to provide an improved optical recording member into which information is written by the selective ablation of a layer of energy absorbing material.